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Hydra lock engine damage?

Old 12-18-2006, 03:38 AM
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foxfoto
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Default Hydra lock engine damage?

I have an OS engine in my Raptor 90. Purchased it from someone who had conducted about 6 ten minute flights. He experienced some starting problems as I have which have resulted in hydra lock. I flew the heli for the 1st time the other day but was only able to get it running after it was totally flooded and am wondering if some engine damage could have ocurred. After about 5 mins of running the engine started acting up, surging in what sounded like a lean condition and when on the ground to check the fuel level and at a medium idle it flamed out when I attmepted to add throttle.

I refueled and approx 2 mins after taking off the engine appeared to flame out at about a 30' hover. I attempted an autorotation but when it was about a foot off the ground I applied full collective on what I thought was a dead engine and it fired back at full throttle (no onboard glow)! Not sure what happened at this point but I am thinking that it folded the mains from the power burst and it crashed falling over on it's side and beating itself for a few seconds until the engine quit.

Is it possible that the head gasket was damaged causing a lean condition? Another possibility is that the fuel valve is damaged and leaking air which I will explore. Want to find the source of my problem prior to flying again to reduce the risk of a repeat of this, it was not pretty... Also for added info I was using a hydrotork starter which also concerns me about an engine damage possibility.

Thanks for any feedback...

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Old 12-18-2006, 12:07 PM
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Default RE: Hydra lock engine damage?

The usual damage from hydraulic lock is a bent connecting rod. This can be detected by turning the engine over with the glow plug removed. The engine will have a stiff spot when it's turned over. If you disassemble the engine, the crank will turn over smoothly, and you can move the piston up and down in the liner smoothly when it's out of the engine. It will have a stiffness when it's assembled.

It's almost impossible to damage the cylinder head gasket if the engine's assembled properly. Hydraulic lock won't do anything to it. You damage the gasket by improper handling when it's outside of the engine, or by an unevenly-tightened head. You can also damage it by an overheat, which would cause the head bolts to go loose and you then get blowby when the engine's running.

The most common problem with helis is fuel foaming...air agitated into the fuel tank by vibration. This causes the engine to go lean. The change in RPM can change the vibration mode, and the foaming can go away. This then causes the engine to surge.

Bench running will allow you to determine if the engine does have a problem, or if it's a result of the engine/airframe combination. Usually, it's the latter.
Old 12-18-2006, 02:46 PM
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Default RE: Hydra lock engine damage?

Hi Bill, Thanks for the info, I feel better that the engine is not damaged. I am about 95% convinced that my problem is a damaged fuel fill valve. I did not have the correct fitting for the TT one and used another brand's nipple. Think it may have damaged the valve which would have caused the engine to suck air instead of fuel. The condition I was experiencing was a lean condition because the engine would race erratically and only momentarily. That would account for why the engine acted like a flameout but came back from idle position to full power when I applied full collective for the auto. When I saw the correct male fitting in the manual while looking up parts it dawned on me what had happened. Expensive lesson. The correct fitting did not come with the heli when I bought it so I substituted another thinking they all were pretty much the same. Will check for binding with the glow plug out though just to be sure. Will be pulling the Defender fuse for a red white and blue paint job anyway...

Thanks! Charlie

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